1. Field of the Invention
The present invention relates to highly purified populations of multipotent mammalian stem cells and progenitor cells, including cardiac stem cells and progenitor cells having the capacity for expansion and differentiation into cardiomyocytes, endothelial cells or smooth muscle cells. The present invention further relates to methods of isolating and expanding multipotent mammalian stem cells and progenitor cells, and therapeutic uses thereof.
2. Description of the Related Art
Ischemic heart disease accounts for 50% of all cardiovascular deaths and is the leading cause of congestive heart failure (reference 1). A new approach to cardiac repair is cellular therapy with stem cells, such as bone marrow-derived mesenchymal stem cells (references 2-4), skeletal myoblast (reference 5), adipose derived mesenchymal stem cells (reference 6), and hematopoietic stem cells (reference 7). Recently, resident cardiac progenitor/stem cells (CSCs) were discovered in the adult heart (references 8-13). Resident CSCs are characterized by their capacity to self-renew in culture, and are multi-potent for forming normal cell types in hearts. Accordingly, they hold great promise for clinical applications, because they are normal components of adult heart and capable of differentiating into cardiomyocyte or vascular lineages.
Previously, populations of cardiac stem cells (c-kit+, Sca-1+) were isolated from adult hearts by cell sorting from enzymatically digested hearts based on cell surface markers (references 8, 9, and 11). However, enzymatic digestion of myocardium compromises the integrity of important surface antigens of resident CSCs and leads to dysfunctional sorted cells, which makes the method hard to be reproduced. More recently, Messina et al. (reference 10) demonstrated that some CSCs migrated from human myocardial biopsies could form cardiospheres that expressed Sca-1, c-kit, Flk, and CD31. However, these cardiospheres contained a mixture of cells, including cardiac fibroblasts, which grow faster than endogenous cardiac stem cells in the cardiosphere. Contamination of resulting cardiospheres with fibroblasts limits the therapeutic use of CSCs prepared from explants, because the contaminating fibroblasts are less efficient for heart repair and may facilitate the scar dilation (reference 14).
Accordingly, there is a need in the art for purified CSCs and substantially free of other cell types, including fibroblasts, as well as improved methods of isolating and expanding multipotent mammalian stem cells and progenitor cells.